I have the TT locking bracket for my eTrex and it has been great especially as you can leave it attached due to the lock. To mount to my bike I used the TT bracket as below as their motorcycle GPS brackets only come with clamps to fit small diameter bars (6 or 8mm IIRC).
http://www.touratech.com/shops/008/p...2c20421f9d7e21
or you could try
http://www.touratech.com/shops/008/p...2c20421f9d7e21
The rubber dampers are good but you do get less choice of where to mount it. If you are feeling rich you could have the TT bracket AND a RAM mount!